Proposal is made for a physician-scientist award directed toward oculomotor physiology. Phase I training includes instruction in neuro-ophthalmology, control systems analysis, electro-oculography and infrared oculography in humans, the use of magnetic search coils an physiological studies in the behaving monkey. During this period, the oculomotor and vestibular literature will be surveyed and assimilated. The experiments proposed are directed at determining the cortical and subcortical contributions to smooth pursuit eye movements and at the link between the slow phases of optokinetic nystagmus (OKN) and pursuit. Three types of study are linked together conceptually. 1) In monkey, lesions of the nucleus of the optic tract (NOT) will be made to assess its role in the generation of OKN, smooth pursuit and saccades to moving targets. 2) In humans with spontaneous cerebral lesions examinations will be performed of pursuit gain bilaterally, saccades to both stationary and moving targets, and OKN. 3) Psychophysical studies of motion perception will be performed in the same human subject population. These will make use of correlated dynamic random noise displays to measure thresholds for motion sensation and will compare motion sensitivity to contrast sensitivity in both hemifields. The aim of these studies is to correlate deficits in visual tracking with deficits in motion perception, thereby assessing the degree to which particular lesions affect the "afferent (i.e. perceptual) limb" or the "efferent (i.e. motor) limb" of pursuit. The lesion studies in monkey are aimed at evaluating the role of the NOT in visual tracking and the degree to which subcortical generation of OKN is linked to pursuit phenomena.